Since the invention of the integrated circuit (IC), the semiconductor industry has experienced continued rapid growth due to continuous improvements in the integration density of various electronic components (i.e., transistors, diodes, resistors, capacitors, etc.). For the most part, this improvement in integration density has come from repeated reductions in minimum feature size, which allow more components to be integrated into a given area.
The past few decades have also seen many shifts in semiconductor packaging that have impacted the entire semiconductor industry. The introduction of surface-mount technology (SMT) and ball grid array (BGA) packages were generally important steps for high-throughput assembly of a wide variety of IC devices, while at the same time allowing for reduction of the pad pitch on the printed circuit board. Conventionally packaged ICs have a structure basically interconnected by fine gold wire between metal pads on the die and electrodes spreading out of molded resin packages. On the other hand, some chip scale packages (CSP) or BGA packages rely on bumps/balls of solder to provide an electrical connection between contacts on the die and contacts on a substrate, such as a packaging substrate, a printed circuit board (PCB), another die/wafer, or the like. Other CSP or BGA packages utilize a solder ball or bump placed onto a conductive pillar, relying on the soldered joint for structural integrity. An underfill material is also typically placed between the IC and the underlying substrate, e.g., packaging substrate, to provide mechanical strength and to protect the IC from environmental contaminants.
In these embodiments, the point of electrical contact between the various substrates is the solder bump. The use of different substrates often means a difference in respective coefficients of thermal expansion (CTE). Due to this difference, the various substrates may expand/contract at different rates as the devices experience temperature cycles. This can create excessive amounts of stress in the joint region that may cause the joint to crack and/or cause other problems, such as delamination issues.